The invention pertains to physical vapor deposition target constructions and to methods of treating physical vapor deposition targets.
Physical vapor deposition methods (which include, for example, sputtering methods) have wide application in fabrication processes when thin films are desired. For instance, sputtering processes are frequently utilized in semiconductor processing applications for forming thin films across a semiconductor substrate.
An exemplary sputtering process is described with reference to FIG. 1. Specifically, an apparatus 10 is shown comprising a physical vapor deposition target 12 above a semiconductor substrate 14. To aid in interpretation of the claims that follow, the terms xe2x80x9csemiconductive substratexe2x80x9d and xe2x80x9csemiconductor substratexe2x80x9d are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
Target 12 has a sputtering surface 15. In operation, ions or atoms (not shown) are impacted against a sputtering surface 15 and utilized to eject material from the sputtering surface toward substrate 14. The ejected material is illustrated by downwardly-directed arrows. The arrows are a standard way of showing ejected material relative to a physical vapor deposition target. An alternative description of the ejected material is to show the material as a cloud 16, since the ejected material generally has an appearance of a mist. The ejected material tends to migrate in three dimensions, rather than simply toward substrate 14, and accordingly, some of the ejected material returns to target 12.
The illustrated apparatus shows target 12 bonded to a backing plate 18. Further, target 12 is shown to comprise a sidewall surface 20 which joins to a periphery of sputtering surface 15. Also, backing plate 18 is shown to comprise a sidewall surface 22 which is coextensive with sidewall surface 20 of target 12. Cloud 16 overlaps surfaces 20 and 22, and accordingly some of the ejected material from sputtering surface 15 is redeposited on sidewall surfaces 20 and 22.
The redeposited material can be problematic in semiconductor device fabrication. In an exemplary process, target 12 comprises titanium, and is sputtered in a nitrogen-containing gas to sputter-deposit a layer of titanium nitride over substrate 14. FIG. 2 illustrates an expanded view of substrate 14 after deposition of titanium nitride over a surface of substrate 14. Specifically, FIG. 2 shows that target 14 has an opening 30 extending therein, and that a deposited titanium nitride film 32 extends over substrate 14 and within opening 30. Opening 30 can ultimately be utilized for fabrication of a semiconductor device. Opening 30 has a width, and a continuing goal of semiconductor device processing is to decrease a width of semiconductor components to enable higher densities of components to be formed over the same footprint of a semiconductor substrate. Accordingly, a continuing goal of semiconductor device fabrication is to enable uniform deposition of thin films within openings having ever-narrower widths. A problem encountered as the width of opening 30 decreases is that small particle contaminants that are non-problematic relative to large openings, become problematic relative to small openings. An exemplary contaminant is a flake 34 shown in FIG. 2, and shown partially occluding opening 30. Flake 34 can be formed from material which has redeposited on sidewall surface 20 of target 12, and subsequently fallen from target 12 onto a surface of substrate 14. Flake 34 can render it difficult, or even impossible, to form a desired device associated with opening 30. Accordingly, it would be desirable to alleviate or prevent flakes of redeposited material from falling from a target surface onto a semiconductor substrate during sputtering operations.
In one aspect, the invent ion encompasses a method of treating a physical vapor deposition target. The target has a sputtering surface and a sidewall edge at a periphery of the sputtering surface. The method comprises pressing a tool against the sidewall edge to form a distribution of imprints in the sidewall edge of the target. The tool is then removed from the sidewall edge, leaving the imprints extending into the sidewall edge.
In another aspect, the invention encompasses a physical vapor deposition target. The target includes a sputtering surface having an outer periphery, and a sidewall edge along the outer periphery of the sputtering surface. The sidewall edge has a repeating pattern of imprints extending therein.